1. Field of Use
This invention will be used in the construction industry, and more particularly in highway and road construction employing a technique known as "Cement Treated Base" or CTB preparation. This CTB preparation method is applicable to both old and new highway and road construction.
2. Prior Art
A current method employed by road builders to prepare a road bed for subsequent topping with concrete or asphalt, includes the initial step of pulverizing the base materials or old road surface, grading the road bed and compacting the base material. When using the "Cement Treated Base" procedure, the next operation includes spraying the road bed soil mixture with dry powered cement, and then adding water to obtain the proper moisture content to the dry cement on the roadbed. This mixture would then be mixed into the compacted road bed/soil mixture base. This base would then be graded, shaped, and compacted to desired height and density, before chemical hydration (and setting of the CTB) occurs. The now in place CTB would then be kept damp for at least six hours.
Chemical hydration is the conversion of liquid water to crystalline water, and provides a strength producing mechanism when concrete sets. Certain chemical mixtures are now available to retard chemical hydration, but still, several problems are encountered in their use in delayed hydration, for example:
a. Variable water to hydration retarder mixture ratio results in inconsistent road bed strength.
b. Nodules of dry cement are not consistently mixed with the applied water and base material, resulting in zones of accelerated chemical hydration that produces localized weaknesses in the road bed.
c. Use of chemical hydration retarders that extend the hydration time, such that water in the mixture evaporates before adequate hydration occurs, reduces road bed strength.
Because of the above problems, the use of retarders, per se, has not resulted in a satisfactory alternate to the CTB method.
In the current conventional CTB procedure, as described hereinbefore, the spraying of dry powered cement over the road bed results in the formation of clouds of toxic, alkaline, high silica dust that are hazardous to the skin, lungs and eyes of humans and animals, and that are damaging to surrounding vegetation, and further create an on going clean-up problem, in addition to being extremely wasteful and expensive.
Many patents have been issued relating to the art of retardation of chemical hydration. Typical of these is U.S. Pat. No. 3,053,673, issued on Sept. 11, 1962, to Wayne A. Walker, and assigned to Halliburton Company, Inc. However, the use of chemical retarders without the use of the method and apparatus of the invention described herein, has not produced the desired results of this invention.